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5 from 13 votes

Magnolia Cookie Cake

Oatmeal chocolate chip cake layers with whipped peanut butter frosting.
Prep Time2 hrs
Cook Time40 mins
Total Time2 hrs 40 mins
Course: Dessert
Cuisine: Cake
Servings: 18 people
Author: Courtney Rich



  • 2 1/2 cups (591.5 g) water
  • 2 1/2 cups (225 g) uncooked old-fashioned oats divided
  • 1 cup (226 g) butter
  • 3/4 cup (150 g) granulated sugar
  • 1 cup (220 g) brown sugar packed
  • 2 teaspoons (8.4 g) vanilla
  • 4 eggs room temperature
  • 1 teaspoon (5.6 g) kosher salt
  • 2 teaspoon (8 g) baking soda
  • 2 teaspoon (5.28 g) cinnamon
  • 3 cups (360 g) all purpose flour
  • 1 cup (150 g) mini chocolate chips


  • 5 cups (625 g) powdered sugar measured and then sifted
  • 1 1/2 cups 3 sticks (339 g) unsalted butter, slightly cold
  • 1 cup (250 g) creamy peanut butter
  • 1 tablespoon (4.2 g) pure vanilla extract
  • 1/4 cup (57.75 g) heavy whipping cream
  • Pinch of coarse salt
  • *This buttercream recipe makes enough to fill and cover your cake. If you want to add additional piping, you’ll want to make an extra 1/2 batch.



  • Preheat your oven to 350 degrees F. Spray three 8-inch or four 6-inch round cake pans with nonstick cooking spray, line the bottoms with parchment paper and spray again. Set aside.
  • In a medium sized pot bring the water to a boil. Add in 2 cups of the oats, stir and remove the pot from the heat. Cover the pot and allow the oats to soak for 20 minutes, until all the water is absorbed. Let the oatmeal cool completely before adding it to the cake batter.
  • In a medium sized mixing bowl, combine the baking soda, salt, cinnamon, and flour. Whisk together. Set aside.
  • In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugars together on medium speed for 2 minutes until light and fluffy. Add in the vanilla and the eggs and mix until combined, scraping the sides of the bowl as necessary.
  • Turn the mixer to low and add in the cooled cooked oats and the flour mixture, mixing until just combined. 
  • Toss the mini chocolate chips in a tablespoon of flour and then stir into the batter, along with the remaining 1/2 cup dry oats.
  • Spread the cake batter into the prepared pans, about 20 ounces of batter in each 8-inch pan or 15 ounces in each 6-inch pan, and bake for 20-22 minutes or until the cake is set in the center and a toothpick comes out with just a few moist crumbs on it. 
  • Allow the cake to cool in the pans for about 5 minutes and then invert onto wire racks to cool completely. Level the cakes.
  • If you're not using the cake layers right away, wrap each layer in plastic wrap. You can freeze them up to a week or up to a month if you also wrap them in foil.


  • In the bowl of electric mixer fitted with the paddle attachment, combine the butter and peanut butter. Beat on medium-high speed until smooth, about 2 minutes.
  • With the mixer on low speed, gradually add the powdered sugar, followed by the vanilla, salt and heavy cream.
  • Turn mixer to medium-high and beat the frosting for about 4 to 5 minutes.
  • Beat frosting by hand with a wooden spoon to get rid of air pockets.


  • On a cake board, spread a small dollop of frosting to hold the cake in place. Place your first of the three cake layers on the board, crumb side up.
  • Spread 1 cup of frosting (with chocolate chips) on the cake layer. Get eye level with the cake to make sure the layer of frosting is applied evenly.
  • Repeat step 2 for the next cake layer and layer of frosting. For the final cake layer, place it top side down, so the smoothest side of the cake (the bottom) is facing up.
  • Cover the entire cake with a thin layer of frosting. Chill the cake for 10 minutes to set the crumb coat and lock in the crumbs. 
  • Once the crumb coat is set, frost the cake with the remaining frosting.